1. Field of the Invention
The present invention relates to armature windings and a dynamo-electric machine using the same, and more particularly, to armature windings suitable for exposure to a varying magnetic field, such as armature windings of a turbine generator, by way of example, and a dynamo-electric machine using the same.
2. Description of the Related Art
Armature windings for conventional turbine generators are described, for example, in U.S. Pat. No. 2,821,641. As illustrated in FIG. 17, in an example described in U.S. Pat. No. 2,821,641, a plurality of strands arranged in multiple tiers are transposed in the middle, and transpose angles of the strands are determined to be 360°, 540°, and the like, as shown in FIGS. 18A, 18B, depending on the power and mechanical dimensions of a particular type of machine for fitting in a slot, such that flux linkages are canceled out within the slot to reduce a loss caused by circulating currents which flow among strands. Specifically, as illustrated in FIG. 17, a strand 11 positioned at the topmost tier of the right row is transposed to the topmost tier of the left row, i.e., on a strand 1 (2n), and right-hand strands 12, 13 positioned at the topmost tier of the right row are sequentially transposed to make the overall winding in a stranded structure. Also, the transpose angle used herein is a 360° transposition in which strands 11, 15 wound from a shaft end I are transposed, and make a round to return to the same positions at a shaft end II, or a 540° transposition in which the strands are transposed further by an extra half cycle. In this event, the angle such as 360° and 540°, and the pitch of transposition are selected such that magnetic fields interlining between windings are canceled out within a fixed iron core 30. For example, the angle and pitch are selected such that a total of magnetic flux φ31 and φ33 interlining between strands 11 and 15 are equal to a magnetic flux φ32 which interlinks in a reverse direction.
JP-A-47-12513 also describes armature windings for a turbine generator. As illustrated in FIG. 19, in this example, two rows of strand group 2 are disposed outside of a strand group 1 transposed over two rows, and strands 21, 22, 23 and the like are interposed to surround the strand group 1. This is intended to reduce a circulating current loss caused by a radial flux φr2.
In U.S. Pat. No. 2,821,641, even though strands are transposed in a strand group, a magnetic flux φ1 interlining at the end I and a magnetic flux φ2 interlining at the end II have the same polarity as each other through a transposition of 360°, so that a magnetic flux (φ1+φ2) interlinks within a closed loop defined by strands 11, 15, and the like. With a transposition of 540°, on the other hand, the magnetic flux φ1 interlinking at the end I of the strands 1, 15 and the magnetic flux φ2 interlining at the end II have the polarities which cancel each other, but the magnetic fields φ1, φ2 are not equal in magnitude because the strands are different in radial position at the end I and end II. In other words, the flux linkage, corresponding to the difference (φ1−φ2) in field strength, remains, thus making it difficult to thoroughly cancel out circulating currents which flow around the strands 11, 15. Thus, there exists not a few current component which circulates among strands.
When a cross-sectional area of strands must be ensured, a winding as shown in FIG. 20 has been used, in which a plurality of transposed strand groups are arranged in parallel. Since such a structure cannot at all cancel out a radial magnetic flux φr2 which interlinks between the strand group 1 and strand group 2, even an increased currents circulate among the strands.
On the other hand, JP-A-47-12513, which is a technique for reducing the radial magnetic flux, involves a complicated structure in which the strand group 2 is arranged in a double configuration to surround the strand group 1, as illustrated in FIG. 19, requiring a large number of manufacturing steps. Also, for example, the strand 11 must be transposed onto a strand 1 (2n), and a strand 21 is further transposed on the step, thus making it difficult to maintain a uniform gap between strands. For this reason, an appropriate insulating strength cannot be maintained.